KR100914279B1 - Catalyst for purifying exhaust gases and process for producing the same - Google Patents

Abstract

The exhaust gas purifying catalyst according to the present invention includes a substrate and a protrusion. The substrate is provided with a direct current gas passage. The protruding portion protrudes at a height of 50 μm or more from the direct current gas passage and includes a precipitate composed of at least one catalytic element selected from the group consisting of alkali metals and alkaline earth metals.

Description

Exhaust gas purification catalyst and its manufacturing method {CATALYST FOR PURIFYING EXHAUST GASES AND PROCESS FOR PRODUCING THE SAME}

The present invention relates to an exhaust gas purifying catalyst capable of efficiently purifying particulate matter (hereinafter referred to as "PM") contained in exhaust gas discharged from a diesel engine, and a manufacturing method thereof. In particular, it relates to a straight-flow catalyst for purifying exhaust gas provided with a plurality of gas passages at which both ends are opened, and a method of manufacturing the same.

In gasoline engines, the harmful components in the exhaust gas have been reliably reduced by strict regulations on exhaust gases and technological developments that can cope with these strict regulations. However, for diesel engines, regulatory and technical developments are less developed than gasoline engines due to the unusual circumstances that harmful components are released as PM.

The following are known exhaust gas purifiers developed for diesel engines. For example, the exhaust gas purifying apparatus can be largely divided into a trapping (or wall flow) exhaust gas purifying apparatus and an open (or direct current) exhaust gas purifying apparatus. Among them, a plug honeycomb structure made of ceramic (ie, a diesel PM filter, hereinafter referred to as "DPF") is known as one of the capture exhaust gas purifying apparatuses. For example, as described in SAE paper, SAE810114, a plugged ceramic honeycomb structure of a DPF is provided with a plurality of cells. Specifically, the cell includes an inlet cell plugged on both downstream ends of the exhaust gas, an outlet cell plugged on both upstream ends of the exhaust gas adjacent to the inlet cell, and a filter partition wall partitioning the inlet cell and the outlet cell. It is made to include. Therefore, the DPF is a wall flow type exhaust gas purifying apparatus that filters the exhaust gas through the pores of the partition wall, and captures PM on the partition wall to suppress the PM from being discharged.

On the other hand, the open exhaust gas purifying apparatus comprises a direct current honeycomb structure provided with a plurality of cells which are open at both ends, similar to a catalyst for purifying exhaust gas emitted from a gasoline engine. The open exhaust gas purifier purifies the PM in contact with the catalyst layer coated on the cell walls.

In DPF, however, the pressure loss increases as PM is deposited thereon. Accordingly, the PM accumulated to regenerate the DPF by a predetermined means must be periodically removed. Accordingly, when the pressure loss increases, conventionally, the accumulated PMs are heated by burning the DPF with a burner or an electric heater or by supplying a high temperature exhaust gas to the DPF to thereby regenerate the DPF. However, in this case, the more the PM is deposited, the higher the temperature increase upon combustion of the deposited PM is. As a result, cases in which the DPF may be damaged by thermal stresses resulting from such combustion may occur.

Accordingly, recently, a continuous regenerative DPF has been developed. In continuous regenerative DPF, a coating layer of alumina is formed on the partition wall of the DPF, and a catalytic element such as platinum group noble metal is loaded on the coating layer. According to the continuous regenerative DPF, since the captured PM is burned by oxidation by the catalytic activity of the catalytic element, it is possible to regenerate the DPF by burning the PM continuously or simultaneously with capturing the PM. Moreover, because the catalytic reaction of the catalytic elements takes place at relatively low temperatures, and since the PM can be burned when they are less captured, continuous regenerative DPFs prevent the DPF from being damaged due to too little thermal stress acting on the DPF. Has the advantage.

In contrast, the direct current catalyst for purifying PM shows less pressure loss, but the PM which is discharged as it is without purification is discharged in large quantities. On the other hand, the wall-flow catalyst for purifying PM may have the disadvantage of showing a larger pressure loss than the direct-flow PM purifying catalyst because the PM is configured to filter when the exhaust gas passes through the partition wall.

Also, Japanese Unexamined Patent Publication (KOKAI) No. 2002-35,583 discloses an exhaust gas purification system comprising a DPF and a combustion catalyst device disposed upstream of the DPF. The combustion catalyst device is provided with a surface that is irregularly shaped to increase the specific surface area so that precious metal is loaded on the irregular-shaped portion. The exhaust gas purification system thus constructed can purify gaseous components such as fuel and hydrocarbons (hereinafter referred to as "HC") not burned by the upstream combustion catalyst device, and capture PM by the downstream DPF. .

However, even in the exhaust gas purifying system disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 2002-35,583, only the irregular-molded portion of the upstream combustion catalyst device exhibits roughness not approximately smaller than 1 m. Accordingly, it is difficult for the upstream combustion catalyst device to completely capture and purify PM. As a result, it is essential to arrange the DPF downstream of the combustion catalyst device. Exhaust gas purification systems require downstream DPFs as a key component and thus cannot solve the problems associated with larger pressure losses.

Accordingly, Japanese Unexamined Patent Publication (KOKAI) No. 2003-326,162 proposes an exhaust gas purifying catalyst comprising a straight-flow substrate, a catalyst layer, heat resistant particles, and a noble metal. The catalyst layer is formed over at least a portion of the partition wall of the direct current substrate. The heat resistant particles are fastened on the catalyst layer and include coarse particles having a particle diameter larger than that of the catalyst layer. The precious metal is included in the catalyst layer. According to the exhaust gas purification catalyst, the PM flowing in the cell of the direct current substrate collides with the coarse particles and is suppressed from flowing. Thus, the PMs stagnate so that they are in a temporarily captured state. The stagnant PM is more likely to come into contact with the catalyst layer with a higher probability, so that it is easy to be purified by the noble metal by oxidation. Accordingly, the exhaust gas purification catalyst exhibits high PM purification performance. Further, the exhaust gas purifying catalyst is basically a direct current type exhaust gas purifying apparatus, although coarse particles protrude from the partition wall in the cell of the direct current base. As a result, the exhaust gas purifying catalyst shows less pressure loss than DPF.

However, the exhaust gas purifying catalyst disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 2003-326,162 is configured so that coarse particles are simply fastened on the catalyst layer. As a result, the exhaust gas purifying catalyst may be separated from the catalyst layer during use. In this case, it is difficult for the exhaust gas purifying catalyst to capture PM. As a result, a problem may arise that the exhaust gas purifying catalyst exhibits reduced PM-purifying performance. Moreover, since the heat resistant particles have no catalytic function, the exhaust gas purification catalyst requires a catalyst layer containing precious metal as a key component.

The present invention was developed in view of the above circumstances. Therefore, the present invention aims not only to provide the gas flow passages with no longcomings such as coming-off and exhibiting long service life, but also essentially providing catalytic function to these protrusions.

The exhaust gas purifying catalyst according to the present invention can achieve the above object. The catalyst according to the present invention is for purifying exhaust gas, comprising: a substrate provided with straight-flow gas-flow passages; And

It protrudes to a height of 50 μm or more from the DC gas flow path, characterized in that it comprises a projection comprising a precipitate (precipitate) consisting of one or more catalytic elements selected from the group consisting of alkali metals and alkaline earth metals.

In the catalyst according to the present invention, it is preferable that a pore opening having a diameter of 10 μm or more may be provided in the direct current gas passage, and the protrusion may be maintained on the direct current gas passage by an anchor effect. It is preferable. Note that the catalyst is formed on the DC gas flow path further comprises a catalyst layer comprising a noble metal, the protrusion is preferably configured to constitute an exhaust gas purifying catalyst according to the invention characterized in that protruding from the catalyst layer. do. In addition, the catalyst according to the present invention preferably further comprises an oxidation catalyst disposed upstream of the exhaust gas flow relative to the catalyst.

Method for producing an exhaust gas purification catalyst according to the present invention,

Loading at least one catalyst element selected from the group consisting of alkali metals and alkaline earth metals in an amount of at least 0.3 mol relative to 1 L of volume of the substrate on a substrate provided in the direct current gas passage; And

And heat-treating the substrate loaded with the catalyst element to deposit a precipitate formed of the catalyst element in order to provide the direct current gas passage with a protrusion protruding at a height of 50 μm or more from the direct current gas passage. It features.

In the production method according to the present invention, it is preferable that a catalyst layer which includes a noble metal and is formed in advance is provided in the DC gas flow path of the substrate.

Accordingly, the catalyst according to the present invention comprises protrusions protruding from the direct current gas passage to a height of 50 μm or more. Accordingly, since the PM flowing in the DC gas passage collides with the protrusions, the flow is suppressed. As a result, it is assumed that the PMs are stagnated in the DC gas flow passages so that they are in a temporarily captured state. Moreover, the protrusions comprise a precipitate consisting of at least one catalytic element selected from the group consisting of alkali metals and alkaline earth metals. Note that the catalytic element has an inherent oxidation activity that enables at least the oxide soot component contained in PM. Therefore, the temporarily captured PM is purified by the catalytic element by oxidation by contacting the catalytic element with an enhanced probability. In addition, even when the protruding portion protrudes into the direct gas flow path, the catalyst according to the present invention shows less pressure loss than the DPF because the substrate of the catalyst according to the present invention is essentially a direct current substrate.

Specifically, the catalyst according to the present invention can exhibit compatible good performance in both PM purifying ability and pressure loss reduction.

In addition, the production method according to the present invention enables to easily and stably prepare the catalyst according to the present invention comprising a protrusion which is one of the characteristics of the present invention.

A more complete understanding of the present invention and its numerous advantages can be better understood with reference to the following detailed description in conjunction with the accompanying drawings and the detailed description, all of which form part of this specification.

1 is a micrograph showing a particulate structure in a radial cross section of a catalyst according to one example of the present invention; And

2 is a micrograph showing a particulate structure in an axial cross section of a catalyst according to one example of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, the general description of the present invention may be further facilitated with reference to specific preferred embodiments, which are provided for purposes of illustration only and are not intended to limit the appended claims.

The exhaust gas purifying catalyst according to the present invention comprises a substrate and a protrusion. The substrate is provided with a direct current gas passage. The protrusion protrudes from the direct current gas passage of the base material. The substrate may comprise one or more members selected from the group consisting of honeycomb shaped substrates, foam substrates and nonwoven substrates, each provided with a plurality of cellular passages. The substrate may be made of a material such as ceramic and a metal exhibiting heat resistance. The ceramic can be made of, for example, cordierite.

Specifically, it is preferable to use a porous substrate formed of ceramic or metallic nonwoven fabric to prepare the substrate. It is preferred that the porous substrate can exhibit an average pore diameter of 10 to 50 μm and a porosity of 10 to 80 volume%. Moreover, it is more preferable that the said porous base material shows the average pore diameter of 10-40 micrometers, and the porosity of 40-80 volume%. Such a porous substrate is provided with pore openings having a diameter of 10 m or more on the surface of the direct current gas passage. In the commonly used water-absorption loading method, the catalytic element is preferably loaded onto the pores by capillary action. Accordingly, the protrusions start from the openings of the pores in the heat treatment process described later in the manufacturing method according to the present invention. As a result, the anchor effect makes it possible to firmly hold the resulting protrusion on the DC gas flow path. Therefore, when the exhaust gas purifying catalyst according to the present invention is in use, the projection part can be suppressed from falling off from the direct current gas passage.

The protrusion protrudes from the direct current gas passage at a height of 50 μm or more. If the height of the protrusions is less than 50 μm, the resulting protrusions are difficult to obtain the function of temporarily capturing PM. On the other hand, if the height of the protrusions is higher than 300 μm, the resulting protrusions will occupy an overgrown volume in the DC gas passage which clogs the DC gas passage, resulting in an undesirably increased pressure loss of the resulting catalyst. . Therefore, it is preferable that the height of the protrusion is 300 m or less. The protrusion may more preferably protrude from a DC gas flow path to a height of 100 to 250 μm, and more preferably, a height of 150 to 250 μm.

The exhaust gas purifying catalyst according to the present invention is preferably arranged such that the catalyst layer can be formed on the direct current gas passage and the protrusion can protrude from the catalyst layer. For example, the catalyst layer may preferably include a porous oxide and a noble metal or a base metal loaded on the porous oxide. It is preferable that the porous oxide can be composed of one or more selected from the group consisting of alumina, zirconia, ceria and titania. Preferably, the precious metal may be composed of one or more selected from the group consisting of Pt, Rh, Pd and Ir. It is preferable that the base metal can be composed of one or more selected from the group consisting of Co, Fe and Cu. The catalyst layer may be disposed in the same manner as the catalyst layer of the conventional oxidation catalyst and three-way catalyst.

The formation density of the protrusions is not particularly limited. However, if the protrusions are formed at a low density, it may be difficult for the protrusions to exhibit the action of temporarily capturing PM. Accordingly, it is preferable to form the protrusions at a high density, and more preferably to form the protrusions at a high density. Furthermore, the protrusions may be selectively formed at various positions according to the forming process. However, it is particularly preferable to form the protrusions uniformly over the entire DC gas flow path. For example, the protrusion may be formed at a forming density of 2 to 20 pieces / mm ² , more preferably 5 to 15 pieces / mm ^2. Is preferred.

The protrusion comprises a precipitate consisting of at least one catalytic element selected from the group consisting of alkali metals and alkaline earth metals. From the standpoint of the degree of PM-oxidation activity and the ease of forming protrusions, it is preferable that the protrusions comprise a precipitate made of an alkali metal, particularly preferably potassium (K); Alternatively, it may be preferable that the protrusion comprises a precipitate made of alkaline earth metal, particularly preferably barium (Ba). To form the protrusions, the catalyst element is loaded onto the substrate in an amount of at least 0.3 mol relative to 1 L volume of the substrate, and then the substrate loaded with the catalyst element is heat treated. If the loading amount of the catalyst element is less than 0.3 mol with respect to 1 L volume of the substrate, the protrusions are insufficiently formed, making it difficult to form protrusions having a height of 50 μm or more. Particular preference is given to loading the catalyst element on the substrate in an amount of at least 0.5 mol relative to 1 L volume of the substrate. On the other hand, if the loading amount of the catalyst element is too large, the protrusion is formed at a height higher than 300 μm. Therefore, it is preferable to load the catalyst element on the substrate in an amount of 5 mol or less for 1 L volume of the substrate, and more preferably in an amount of 1 mol or less for 1 L volume of the substrate. It is further noted that the loading amount of the catalyst element is more preferably in the range of 0.5 to 2 mol with respect to 1 L volume of the substrate, and most preferably loading in the amount of 0.5 to 1 mol.

In addition, when the catalyst layer is additionally provided to the exhaust gas purifying catalyst according to the present invention, the amount of the catalyst element comprising at least one selected from the group consisting of alkali metals and alkaline earth metals, based on the amount of 4 mol or more, per 1 kg weight of the catalyst layer It is preferable to load with. When the loading amount of the catalyst element is less than 4 mol with respect to the weight of 1 kg of the catalyst layer, the protrusions are not easily formed and it is difficult to form the protrusions having a height of 50 μm or more. Note that the catalyst element may be loaded onto the catalyst layer after forming the catalyst layer, or may be loaded into the catalyst layer at the same time as the formation of the catalyst layer. Further, the catalyst element may be loaded in an amount of 4 mol or more and 50 mol or less, and more preferably 6 mol or more and 15 mol or less, based on 1 kg of the catalyst layer.

Subsequent to the process of loading the catalyst element, the process of heat-treating the substrate loaded with the catalyst element may be carried out in air. In this case, it is preferable that the substrate loaded with the catalyst element can be heat treated at a temperature in the range of 200 to 600 ° C, more preferably 300 to 500 ° C. If the heat treatment temperature is lower than 200 ° C., the growth rate of the protrusions is so slow that it takes a long time to form protrusions having a height of 50 μm or more. On the other hand, if the heat treatment temperature is higher than 600 ° C., a case may occur in which protrusions are not formed because the catalyst element may react with or dissolve in the substrate.

Since the protrusion of the exhaust gas purification catalyst according to the present invention comprising at least one member selected from the group consisting of alkali metals and alkaline earth metals comprises a catalytic element, the simple exhaust gas purification catalyst according to the present invention is characterized in that the oxidation activity is You may suffer from the disadvantage that high NO ₂ is not likely to occur. Accordingly, it is preferable that the exhaust gas purification catalyst according to the present invention may further be provided with an oxidation catalyst disposed upstream of the exhaust gas flow relative to the simple exhaust gas purification catalyst according to the present invention. When the exhaust gas purifying catalyst according to the present invention is thus configured, NO ₂ generated by the oxidation catalyst flows into the simple exhaust gas catalyst according to the present invention. Therefore, the oxidation of the PM which the protrusion temporarily captures is further promoted. In particular, in the low temperature region lower than 300 ° C, the catalytic element comprising at least one member selected from the group consisting of alkali metals and alkaline earth metals hardly exhibits PM oxidation activity. Also from this point of view, it is preferable that NO ₂ in which the oxidation catalyst is generated compensates for the oxidation of PM to which the catalytic element acts. It is noted that the oxidation catalyst may preferably comprise a direct current structured substrate, a coating layer formed on the direct current structured substrate and an oxidation catalyst element loaded on the coating layer. The coating layer is preferably made of one or more selected from the group consisting of alumina, titania and zeolite, and may be formed in an amount of 10 to 200 g with respect to 1 L of the DC-structured substrate, 20 to 100 g More preferably, it can be formed in an amount of. The oxidation catalyst element may be made of one or more selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt), It is preferred that it can be loaded in an amount of 0.1 to 10 g with respect to 1 L of the direct current structured substrate, and more preferably it can be loaded in an amount of 0.5 to 5 g.

Examples

Hereinafter, the exhaust gas purifying catalyst according to the present invention will be described in more detail with reference to specific examples and comparative examples.

(First embodiment)

Honeycomb substrates were prepared. Note that the honeycomb substrate is made of cordierite and has a volume of 2L. Moreover, the honeycomb substrate comprises cells in an amount of 300 cells / in ² and exhibits an average pore diameter of 25 μm and a porosity of 65 vol%. The honeycomb substrate is also for use in DPF applications and includes gas permeable barriers. However, since no plug is provided in the honeycomb base material, the honeycomb flow path has a direct current honeycomb structure. The honeycomb substrate is immersed in an alumina sol exhibiting a primary particle diameter in nm. The honeycomb substrate is then taken out of the alumina sol and blown off with excess alumina sol. The honeycomb substrate is then dried at 120 ° C. and further calcined at 500 ° C. for 2 hours. Thus, an alumina coating layer is formed on and within the honeycomb substrate. Note that the alumina coating layer is formed in a small amount of 35 g per 1 L volume of the honeycomb substrate, and is formed not only inside the pores but also on the partition wall.

Subsequently, the honeycomb substrate provided with the alumina coating layer is impregnate with a predetermined amount of aqueous platinum dinitrodiamine solution having a predetermined concentration. Thereafter, the honeycomb substrate is dried at 120 ° C and further calcined at 500 ° C for 1 hour. Thus, Pt is uniformly loaded on and within the aluminum coating layer in an amount of 2 g relative to 1 L volume of the honeycomb substrate.

Moreover, the honeycomb substrate loaded with Pt on the aluminum coating layer is impregnated with a predetermined amount of aqueous potassium acetate solution having a predetermined concentration. Thereafter, the honeycomb substrate is dried at 120 ° C and further calcined at 500 ° C for 1 hour. Thus, K is loaded onto and within the aluminum coating in an amount of 0.5 mol relative to 1 L volume of the honeycomb substrate.

Finally, the resulting honeycomb substrate is heat treated at 650 ° C. in air for 20 hours. Thus, the catalyst according to the first embodiment of the present invention is produced. 1 and 2 are micrographs showing a cross section of the catalyst according to the first embodiment. Specifically, Figure 1 is a micrograph showing a cross section cut in the radial direction of the catalyst according to the first embodiment, the cross section of the partition and the partition is observed. Moreover, FIG. 2 is a micrograph showing the cross section cut in the axial direction of the catalyst according to the first embodiment, and is focused on the partition faces observed between the cut partition walls.

It can be seen that the bulkhead face is provided with a number of protrusions projecting into the barrier. Moreover, the protrusions have a height of 50 μm or more, and there are also protrusions whose height is approximately 200 μm. In addition, the protrusion is grown from the pores of the partition wall, it can be seen that it is firmly held on the partition wall by the anchor effect. Note that the results of the elemental analysis show that the protrusions mostly consist of K, specifically potassium carbonate or potassium oxide.

(Comparative Example 1)

Honeycomb substrates were prepared. Note that the honeycomb substrate is made of cordierite and has a volume of 2L. Moreover, the honeycomb substrate comprises cells in an amount of 400 cells / in ² and exhibits an average pore diameter of 3 μm and a porosity of 25 volume%. It is also noted that the prepared honeycomb substrate is for a conventional oxidation catalyst or three-way catalyst and does not contain any gas-permeable partition walls.

A slurry is wash-coated on the honeycomb substrate. Note that the main components of the slurry are 80 parts by weight of alumina and 70 parts by weight of zeolite. The wash-coated honeycomb substrate is dried and calcined in the same manner as in the first embodiment. Thus, a coating layer is formed on the honeycomb substrate. Note that the coating layer is formed in an amount of 150 g per 1 L volume of the honeycomb substrate. Finally, using an aqueous platinum dinitrodiamine solution, Pt is loaded onto the honeycomb substrate in an amount of 2 g per 1 L volume of the honeycomb substrate.

(Comparative Example 2)

A catalyst according to Comparative Example 2 was prepared in the same manner as in Example 1, except that potassium (K) was not loaded on the honeycomb substrate.

(Comparative Example 3)

A catalyst according to Comparative Example 3 was prepared in the same manner as in Example 1, except that the honeycomb substrate loaded with Pt and K on the alumina coating layer did not undergo heat treatment.

Second Embodiment

The same manner as in Comparative Example 1, except that the coating layer was formed in an amount of 200 g with respect to 1 L of the honeycomb base material, and was disposed upstream of the exhaust gas flow for the catalyst according to the first embodiment. The catalyst is prepared. The combination of the resulting catalyst and the catalyst according to the first embodiment was named the catalyst according to the second embodiment of the present invention.

(Comparative Example 4)

The same manner as in Comparative Example 1, except that the coating layer was formed in an amount of 200 g with respect to 1 L of the honeycomb base material, and was disposed upstream of the exhaust gas flow for the catalyst according to the first embodiment. The catalyst is prepared. The combination of the resulting catalyst and the catalyst according to the first comparative example was named as the catalyst according to the fourth comparative example.

(Test and evaluation)

The catalysts according to the first and second embodiments and the first to fourth comparative examples were installed in the engine bench test apparatus. Specifically, the catalysts were respectively connected to the exhaust pipe of the 2L displacement diesel engine equipped with the engine bench test apparatus. Thereafter, the diesel engine was operated in EC mode for 4 cycles. The catalysts were examined for PM reduction rates for each of four cycles. The catalysts were evaluated in terms of the rate of PM reduction averaged over four cycles. Table 1 below summarizes the evaluation results. Moreover, the maximum pressure loss exhibited by the catalysts was measured when the diesel engine was operated in EC mode for 4 cycles. Table 1 also summarizes these measured results. Note that the PM reduction rate is obtained by calculating the ratio of the PM weight emitted from the catalysts for each of the four cycles to the total PM emission weight from the diesel engine for each of the four cycles.

K Heat treatment PM reduction rate (%) Pressure loss (kPa) First embodiment include U 22 2.3 Comparative Example 1 none radish 5 1.6 Comparative Example 2 none U 11 2.0 Comparative Example 3 include radish 12 2.1 Second embodiment include U 28 3.9 Comparative Example 4 none radish 8 3.2

From Table 1, it can be seen that the catalyst according to the first embodiment showed a higher PM reduction rate than the catalysts according to the first to third comparative examples. Similarly, it can be seen that the catalyst according to the second embodiment also shows a higher PM reduction rate than the catalyst according to the fourth comparative example. It is evident that the catalysts according to the first and second embodiments have advantages because the projections are provided. Note that the catalysts according to the first and second embodiments showed an increased maximum pressure loss because the projections were provided. However, this increased maximum pressure loss is not a problem when the catalysts according to the first and second embodiments are actually applied.

Moreover, the catalyst according to the second embodiment exhibited an improved average PM reduction rate than the catalyst according to the first embodiment. The difference between the average PM reduction rate indicated by the catalyst according to the fourth comparative example and the average PM reduction rate indicated by the catalyst according to the first comparative example, that is, 3%, is exhausted from the catalyst according to the second example with respect to the catalyst according to the first example. The additional oxidation catalyst added upstream of the gas flow is equivalent to the indicated PM reduction rate. However, the average PM reduction rate 28% indicated by the catalyst according to the second embodiment is greater than the simple sum of 3% with the average PM reduction rate indicated by the catalyst according to the first embodiment. This fact suggests that the catalyst according to the second embodiment exhibits a useful synergistic effect. In addition, the catalyst according to the second embodiment shows a significantly higher average PM reduction rate than the catalyst according to the fourth comparative example. This advantage is that the NO ₂ generated in the additional oxidation catalyst disposed upstream of the exhaust gas flow with respect to the simple catalyst according to the first embodiment flows into the simple catalyst according to the first embodiment, so that even in a low temperature region of about 250 ° C. or more. This is due to the fact that the resulting NO ₂ will promote oxidation of the PM which is temporarily captured on the protrusions.

The exhaust gas purifying catalyst according to the present invention can be applied to the purification of exhaust gas emitted from an internal combustion engine such as a diesel engine, and in particular to the purification of exhaust gas containing PM.

Claims (12)

In the exhaust gas purification catalyst, A substrate provided with straight-flow gas-flow passages; And Protruding to a height of 50 ㎛ or more from the DC gas flow path, comprising a projection comprising a precipitate (precipitate) consisting of at least one catalytic element selected from the group consisting of alkali metals and alkaline earth metals, The projecting catalyst is characterized in that the exhaust gas purifying catalyst is formed integrally with the DC gas flow path of the substrate. The method of claim 1, The DC gas flow passage is provided with a pore opening having a diameter of 10 μm or more, The projecting catalyst is characterized in that the projection is held on the DC gas flow path by the anchor effect (anchor effect). The method of claim 1, It is formed on the DC gas flow path further comprises a catalyst layer comprising a noble metal, And the protrusion protrudes from the catalyst layer. The method of claim 1, And an oxidation catalyst disposed upstream of the exhaust gas flow with respect to the catalyst. The method of claim 1, The substrate is an exhaust gas purification catalyst, characterized in that it comprises a porous substrate. The method of claim 5, The porous substrate is an exhaust gas purifying catalyst, characterized in that it exhibits an average pore diameter of 10 to 50 ㎛ and porosity of 10 to 80% by volume. The method of claim 1, The projecting portion of the exhaust gas purifying catalyst, characterized in that protruding from the DC gas flow path to a height of more than 50 ㎛ ~ 300 ㎛. The method of claim 1, Wherein said catalyst element is loaded onto said substrate in an amount of at least 0.3 mol and up to 5 mol with respect to 1 L volume of said substrate. The method of claim 3, Wherein said catalyst element is loaded in an amount of at least 4 mol with respect to 1 kg of weight of said catalyst bed. In the method for producing the exhaust gas purification catalyst, One or more catalytic elements selected from the group consisting of alkali metals and alkaline earth metals are loaded on a substrate provided in a straight-flow gas-flow passage in an amount of at least 0.3 mol per 1 L volume of the substrate. fair; And Heat treating the substrate loaded with the catalyst element to deposit a precipitate formed of the catalyst element in order to provide a protruding portion protruding at a height of 50 μm or more from the direct current gas passage to the direct current gas passage; By the way, And the protrusion is integrally formed with the direct current gas flow passage of the substrate. The method of claim 10, The method for producing an exhaust gas purifying catalyst, characterized in that the direct current gas flow passage is provided with a catalyst layer containing a noble metal and formed in advance. The method of claim 10, The substrate loaded with the catalyst element is a method for producing an exhaust gas purifying catalyst, characterized in that the heat treatment at a temperature in the range of 200 to 600 ℃.

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